In order to maintain a plurality of circuit breakers, it is necessary to have permanently updated information about the state of wear of each of the circuit breakers.
Methods are known that enable circuit breaker wear to be estimated by measuring interrupted current.
Studies have shown that circuit breaker wear is proportional to the sum of the integrals over the duration of the arc, of the square of each interrupted current.
A first method consists in measuring the value of the current immediately prior to the circuit breaker opening (e.g. the peak current) and in accumulating over the lifetime of the circuit breaker the squares of the amps that have been interrupted.
That method is relatively easy to implement, but it is not accurate, since although it takes account of the magnitude of the interrupted current, it does not take account of the time actually taken by the circuit breaker to interrupt the current.
It is possible to use another method that is more accurate but more difficult to implement, in which, for each pole of a given circuit breaker, the integral of the square of the current interrupted by the current breaker is calculated over the successive operating times of the circuit breaker.
That method is considered as being difficult to implement since it requires accurate knowledge of the (short) length of time during which arcing actually takes place.
It is possible, for example, to monitor the presence of an arc by means of a system that makes use of an optical fiber and a photoelectric cell. However that solution is very expensive for a circuit breaker of new design and it is totally inapplicable to circuit breaker models that are already in existence.